Remote control system



Patented Nov. 5, i946 REMOTE CONTROL SYSTEM James W. Conklin,Indianapolis, Ind., assignor to Radio Corporation of America, acorporation of Delaware Application February 24, 1943, Serial No.476,902

4 Claims. c1. 172-239) l Ihis invention relates to electrical servosystems of the follow-up type and more particularly to the prevention ofoperation of the control member of such systems at a rate exceeding themaximum speed capability of the driving motor. The usual servo systemcomprises a control input shaft, an output shaft, means for producingcontrol voltage related in some predetermined manner to the differencein the angular positions of 'saidshaits and a driving motor controlledby ly falls out of synchronism with the control shaft.

The principal object of the present invention is to provide an improvedmethod of and means for limiting the rate of operation of the controlmember of a servo system to prevent operation of the control at a rateexceeding the capabilities of the driven device.

Another object is to provide an improved method of and means forlimiting the angle of lag of the output shaft with respec-t to thecontrol shaft.

A further object is to providelimproved means for controlling the speedof operation of the control input shaft of a servo system in response tothe angular displacement between the input and output shafts. These andother and incidental objects will become apparent to those skilled inthe art upon consideration of the following description with referenceto the accompanying drawing which ls a schematic circuit diagram of aservo system embodying the present invention.

An A,C. motor I is mechanically connected to the load device 3, and tothe rotor of asynchro transformer 5. The rotor o1' the transformer 5 iselectricallir connected to an amplifier I which is connected to theinput circuit of themotor I.

- "The stator winding of the transformer 5 is electrically connected tothe stator windingof a second synchro transformer S. The rotor windingof the transformer 9 is connected to an A.-C. supply. not shown. Therotor of the transformer is mechanically coupled to a control devicesuch as a manually operable crank I I.

The system as thus far described constitutes a conventional servo systemof the follow-up type.

In operation, the control member II is moved to an angular positioncorresponding to that to which it is desired to operate the drivendevice 3. Alternating current is transmitted through .the cascadedsynchro transformers 5 and 9 to the input circuit of the amplifier l.VThe amplitude of the input voltage to the amplifier 1 is directlyproportional lto the difference in the angular positions of the rotorsof -the transformers 5 and 9. This voltage is amplified and is appliedto the motor I, driving the output shaft, and with it the device 3 toVsuch a position that .the rotor of `the transformer 5 corresponds inangular position with the rotor of the transformer 9. When thiscondition is attained the voltage applied to the input circuit oi theampliiler "i is zero, and the motor I is deenergized.

Ordinarily, the driving motor is of the induction or repulsion type, andhence cannot operate above a predetermined speed, corresponding to thesynchronous speed. This speed depends upon construction o1' the motorand upon the frequency of the A.C. supply. As mentioned above it isundesirable to operate the control shaft at a speed approaching thesynchronous speed of the driving motor because of the resultant increasein lag, and the possibility that the driven shaft may fall out of stepwith the control member. Accordingly, an A.-C. motor I3 is mechanicallycoupled to the control shaft and electrically connected to Ithe outputof the synchro transformer 5. The coupling between the motor I3 and therotor of the control transformer 9 includes gearing I5, so designed thatthe synchronous speed of the motor I3 will occur at a speed of rotationof .the control member I I which is somewhat less than the synchronousspeed of the driving motor I. In the normal operation of the system theoutput voltage of the transformer 5 is of the order of1 percent of theA.C. supply voltage. This voltage,

when applied to the motor I3, will produce sub-y stantially no effect.However, when the angular lag between the rotor of the transformer 5 andthat of the transformer 9 4approaches 90, the

Thus the invention has been described-as an l improved electrical servosystem of the follow-up type, including means for preventing theoperation of the control input member at a rate greater than apredetermined fraction of the synchronous speed of the driving motor.This is accomplished by coupling an auxiliary A.C. motor to the inputshaft, and connecting said motor to the electrical control channel ofthesystem. The arrangement is such that the auxiliary motor reachessynchronism at a lower speed of operation of the control shaft than thedriving motor. At synchronous speed of the auxiliary motor, a stronglock-in torque is developed, effectively preventing any further increasein speed.

I claim as my invention:

i. A remoto control system including a driven shaft, a control shaft,means for deriving an A.C. control voltage proportional in amplitude tothe difference in the angular positions of said shafts, a control memberconnected to said control shaft and to an A.C. motor. and means forapplying said A.C. voltage to said motor so' as .to prevent operation ofsaid control member above a predetermined speed.

2. In a remote control system of the follow-up type. `comprising -adriving motor, a load shaft `connected to said motor, a control shaftand means for deriving a control signal related in a predeterminedmanner to the difference in the angular positions of said shafts, amotor coupled to said control shaft and connected to respond to saidcontrol signal so as to prevent operation of said control shaft at aspeed exceeding the maximum speed of said driving motor.

3. A servo system comprising a driving motor, an output shaft coupled tosaid motor, a synchro transformer coupled to said output shaft, anampliier connected between the rotor winding of said synchro transformerand said driving motor, a second synchro transformer with its statorvwinding connected to the stator winding of said first synchrotransformer and its rotor coupled to a control shaft, a source of A.C.energy connected to -the rotor winding of said second synchrotransformer, and -an A.C. motor coupled to said control shaft andconnected to the rotor of said first synchro transformer.

4. 'I'he invention as set forth in claim 3 wherein said A.C. motor iscoupled to said control shaft in such a manner that .the rate ofrotation of said A.C. motor is a greater fraction of the synchronousspeed of said motor than the speed of said driving motor is of thesynchronous speed of said driving motor.

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